Large Accessory Navicular Bone

Overview
An accessory navicular bone is an accessory bone of the foot that occasionally develops abnormally causing a plantar medial enlargement of the navicular. The accssory navicular bone presents as a sesamoid in the posterior tibial tendon, in articulation with the navicular or as an enlargment of the navicular. Navicular (boat shaped) is an intermediate tarsal bone on the medial side of the foot. It is located on the medial side of the foot, and articulates proximally with the talus. Distally it articulates with the three cuneiform bones. In some cases it articulates laterally with the cuboid. The tibialis posterior inserts to the os naviculare. The tibialis posterior muscle also contracts to produce inversion of the foot and assists in the plantar flexion of the foot at the ankle. Tibialis posterior also has a major role in supporting the medial arch of the foot. This supports is compromised by abnormal insertion of the tendon into the accessory navicular bone when present. This lead to loss of suspension of tibialis posterior tendon and may cause peroneal spastic pes planus or simple pes planus. But, yet a cause and effect relationship between the accessory navicular and pes planus is doubtful and is yet unproved clearly.



Causes
Like all painful conditions, ANS has a root cause. The cause could be the accessory navicular bone itself producing irritation from shoes or too much activity. Often, however, it is related to injury of one of the structures that attach to the navicular bone. Structures that attach to the navicular bone include abductor hallucis muscle, plantar calcaneonavicular ligament (spring ligament) parts of the deltoid ligament, posterior tibial tendon.

Symptoms
The catalyst for symptoms might be some sort of injury (such as a broken or sprained ankle), excessive activity, or irritation from where shoes are rubbing on the bony prominence the accessory navicular makes. These can irritate the bone, or make the tendon it?s embedded in (the posterior tibial tendon, remember?) inflamed and sore. Because the tendon is compromised in its ability to support the arch, accessory navicular syndrome almost always leads to flat feet, which is one very obvious symptom.

Diagnosis
To diagnose accessory navicular syndrome, the foot and healthy salads ankle surgeon will ask about symptoms and examine the foot, looking for skin irritation or swelling. The doctor may press on the bony prominence to assess the area for discomfort. Foot structure, muscle strength, joint motion, and the way the patient walks may also be evaluated. X-rays are usually ordered to confirm the diagnosis. If there is ongoing pain or inflammation, an MRI or other advanced imaging tests may be used to further evaluate the condition.

Non Surgical Treatment
Although operative treatment, and removal of the accessory navicular is possible, this is not usually indicated at first. Conservative nonoperative treatment is best, the course depending on the severity of the symptoms. When the pain is very severe, which could indicate a fracture, a period of immobilization might be required. This is done by waring a fracture boot, or a cast, which can help the ossicle stay stable, aiding in healing. Immobilization usually lasts between 4 to 6 weeks. Afterwards, physical therapy exercise, or any appropriate home course, should be used to help strengthen the ankle and return the ankle and foot to full range of motion, and have no pain on movement. Sometimes crutches are used when weight bearing is too painful, but it is best to try to bear weight when possible.



Surgical Treatment
If non-surgical treatment fails to relieve the symptoms of accessory navicular syndrome, surgery may be appropriate. Surgery may involve removing the accessory bone, reshaping the area, and repairing the posterior tibial tendon to improve its function. This extra bone is not needed for normal foot function.